U.S. patent number 4,682,853 [Application Number 06/844,051] was granted by the patent office on 1987-07-28 for transmission projection screen and method of manufacturing same.
This patent grant is currently assigned to U.S. Philips Corporation. Invention is credited to Dirk J. Broer, Cornelis M. G. Jochem, Renso J. M. Zwiers.
United States Patent |
4,682,853 |
Broer , et al. |
July 28, 1987 |
Transmission projection screen and method of manufacturing same
Abstract
The invention relates to a transmission projection screen having
a high light output and a suitable contrast, for example, for use
in a projection-television system, and a method of manufacturing
such a screen. The projection screen comprises a transparent
substrate having a front surface which is provided with mutually
parallel ribs. Light-absorbing glass fibers 10 are provided at the
bottom of the grooves 24 between the ribs 22, and they are fixed by
means of a hot-melt adhesive layer 11.
Inventors: |
Broer; Dirk J. (Eindhoven,
NL), Zwiers; Renso J. M. (Eindhoven, NL),
Jochem; Cornelis M. G. (Eindhoven, NL) |
Assignee: |
U.S. Philips Corporation (New
York, NY)
|
Family
ID: |
19847401 |
Appl.
No.: |
06/844,051 |
Filed: |
March 26, 1986 |
Foreign Application Priority Data
|
|
|
|
|
Jan 10, 1986 [NL] |
|
|
8600043 |
|
Current U.S.
Class: |
359/453;
359/456 |
Current CPC
Class: |
G03B
21/625 (20130101) |
Current International
Class: |
G03B
21/62 (20060101); G03B 021/60 () |
Field of
Search: |
;350/128 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Wintercorn; Richard A.
Attorney, Agent or Firm: Briody; Thomas A. Streeter; William
J. Rich; Marianne R.
Claims
What is claimed is:
1. A transmission projection screen comprising a transparent
substrate having a front surface which is provided with mutually
parallel ribs from which light issues during operation of the
screen, grooves being present between the successive ribs, in which
grooves light-absorbing thread-like elements are disposed,
characterized in that the light-absorbing elements are made from
glass fibres.
2. A transmission projection screen as claimed in claim 1,
characterized in that the glass fibres consist of black glass.
3. A method of manufacturing a transmission projection screen as
claimed in claim 1 or 2, characterized in that the method comprises
the following steps:
a light-absorbing glass fibre is covered with a synthetic resin
cladding,
synthetic resin cladded glass fibres are disposed in the grooves of
the screen,
the screen including the glass fibres is subjected to a treatment
such that the synthetic-resin cladding adheres to the walls of the
grooves.
4. A method as claimed in claim 3, characterized in that the
treatment to make the synthetic resin cladding adhere is a heat
treatment.
5. A transmission projection screen, comprising
a transparent substrate having a surface having a plurality of ribs
separated by grooves; and
a multiplicity of glass fibers each having a predetermined
cross-section and a predetermined color disposed in said plurality
of grooves for absorbing ambient light falling on said screen.
6. A transmission projection screen as claimed in claim 5, wherein
said predetermined color is black.
7. A transmission projection screen as claimed in claim 5, wherein
said cross-section is circular.
8. A transmission projection screen as claimed in claim 5, further
comprising a coating covering at least part of each of said glass
fibers.
9. A transmission projection screen as claimed in claim 8, wherein
said coating is a synthetic resin coating.
10. A transmission projection screen as claimed in claim 5, wherein
at least one of said glass fibers is disposed in each of said
plurality of grooves.
11. A transmission projection screen as claimed in claim 5, wherein
said grooves are V-shaped having a narrow and a wide portion; and
wherein said glass fibers have a diameter fitting into said narrow
portion.
12. A method for creating blackening in manufacturing a
transmission projection screen having a plurality of ribs separated
by grooves, comprising the steps of
manufacturing a glass fiber having a predetermined color and
cross-section;
coating said glass fibers at least in part with an adhesive
coating; and
placing said glass fibers with said coating into said grooves.
13. A method as claimed in claim 12, wherein said predetermind
color is black.
14. A method as claimed in claim 12, wherein said coating step
comprises coating said glass fibers with a synthetic resin;
further comprising the step of heat treating said glass fiber with
said coating after placement into said grooves thereby coating a
bond between said glass fibers and said grooves.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a transmission projection screen
comprising a transparent substrate having a front surface which is
provided with mutually parallel ribs from which light issues during
operation of the screen, grooves being present between the
successive ribs, in which grooves light-absorbing thread-like
elements are disposed.
The invention also relates to a method of manufacturing a
transmission projection screen.
2. Description of the Prior Art
Such a screen is used, for example, for displaying images or
alphanumeric data which are projected on the rear surface of the
screen, for example, by a lens system with one or more cathode ray
tubes or by a film projector. The transparent ribs situated on the
front surface focus the light rays which are received from the rear
side and which issue via the apexes of the ribs. The grooves
between the ribs remain dark. In order to avoid reflection of
ambient light from both the front side and the rear side of the
screen, which would reduce the contrast of the image to be
displayed, a light-absorbing material is disposed in the grooves.
It is known that for this purpose a black lacquer layer can be
applied or that black particles are disposed in the grooves. A
disadvantage of such screens is the high degree of mechanical
contact and, thus, optical contact between the ribs and the
light-absorbing material, which causes light that should be
reflected on the inside of the walls of the ribs to be absorbed,
thereby reducing the light output of the screen.
U.S. Pat. No. 4,525,029 describes a transmission projection screen
and a method of manufacturing such a screen, in which method black
wires, for example, of yarn, metal or synthetic resin are
introduced into the grooves. The black wires are longitudinally
introduced into the grooves, during and/or after which operation
the wires are under tension to make sure that they are in the
grooves over their full length. The wires are fixed by means of,
for example, glue. A disadvantage of such a screen is that it may
be subject to warpage, for example, due to changing ambient
conditions, humidity being a particularly important factor
therein.
It is an object of the invention to provide a transmission
projection screen which is not or hardly subject to warpage caused
by changes in humidity and/or temperature. For this purpose, it is
an object of the invention to provide a transmission projection
screen in which the light-absorbing wires do not have to be under
tension during or after their insertion. A further object of the
invention is to provide a transmission projection screen having an
aesthetically attractive, smooth front surface. A particular object
of the invention is to provide a transmission projection screen
having a flat or substantially flat front surface, the
light-absorbing wires being situated deeply in the grooves over
their full length so as not to catch the light issuing from the
apexes of the ribs.
This object is achieved in accordance with the invention by a
transmission projection screen as described in the opening
paragraph, which screen is further characterized in that the
light-absorbing elements are made of glass fibers.
Due to the great rigidity of glass, glass fibres can be deeply
inserted into the grooves over their full length without being
under tension. Thanks to the use of glass fibres an aesthetically
attractive screen is obtained having straight and regular
light-absorbing lines.
The surface of the glass fiber may be provided, for example, with a
black layer. In a particularly suitable embodiment of the
projection screen in accordance with the invention, the glass fiber
consist of black glass.
The use of glass fibers has the additional advantage that the
diameter of a glass fiber may be chosen within wide limits and may
be adapted to the dimensions of the grooves in order to make sure
that the glass fiber fits in the lower part of a groove, while
having a sufficiently large diameter to substantially reduce the
light reflection at the front side of the screen. By making sure
that the contact area between the glass fibers and the walls of the
grooves is small, it is possible to obtain only a marginal
reduction in the light output of the screen.
An additional object of the invention is to provide a method of
manufacturing a transmission projection screen, in which the
light-absorbing elements can be readily fixed in the grooves.
This object is achieved in accordance with the invention by a
method which is characterized in that it comprises the following
steps:
a light-absorbing glass fiber is covered with a synthetic resin
coating,
synthetic resin coated glass fibers are disposed in the grooves of
the screen,
the screen including the glass fibers is subjected to a treatment
which causes the synthetic resin coating to adhere to the walls of
the grooves.
Such a treatment may consist in, for example, contacting the screen
with the vapour of a solvent for the synthetic resin of the
synthetic resin coating.
In a very suitable embodiment of the method in accordance with the
invention, the treatment for making the synthetic resin coating
adhere is a heat treatment. In this case, the synthetic resin
coating consists of a glue whose adhesive action is obtained by
heating and subsequent cooling, a so-called "hot-melt" adhesive. An
important advantage of this embodiment of the method is that glass
fibers may be used which are provided with a synthetic resin
coating in a separate treatment and which at some later time, for
example after storage, are used in the actual manufacture of the
screen, which is usually carried out in a clean room. Consequently,
chemicals such as adhesive, solvents or black powdered material for
providing the grooves of the projection screen with light-absorbing
material do not have to be used in the clean room.
BRIEF DESCRIPTION OF THE DRAWING
An exemplary embodiment of the screen and the method in accordance
with the invention are explained in more detail with reference to a
drawing, in which
FIGS. 1a and 1b are sectional views of a glass fiber without and
with a synthetic resin coating, respectively, which fiber may
suitably be used in a screen in accordance with the invention,
FIG. 2 is a perspective and sectional view of a substrate provided
with ribs, for use in a screen in accordance with the invention,
and
FIG. 3 is a sectional view of a screen in accordance with the
invention, a glass fiber being represented in one of the
grooves.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A glass fiber is manufactured in a way which is known per se, for
example, by drawing from a preform or from molten glass contained
in a crucible which has a discharge opening at the bottom. The
glass composition is so selected that the glass fiber has a black
colour. A suitable glass composition comprises, for example, 60.2%
by weight of SiO.sub.2, 16.8% by weight of B.sub.2 O.sub.3, 7.5% by
weight of K.sub.2 O, 3.3% by weight of Al.sub.2 O.sub.3, 0.4% by
weight of Na.sub.2 O, 0.8% by weight of Li.sub.2 O, 2.7% by weight
of V.sub.2 O.sub.5 and 8.3% by weight of Fe.sub.2 O.sub.3, which
glass composition can be drawn from a preform into a fiber at a
temperature of 675.degree. C. The cross-section of the fiber may
have any suitable shape, provided that it is selected so that the
contact area with the walls of the grooves is small. To facilitate
the insertion of the fiber, suitably, a fiber having a circular
cross-section is used, see FIG. 1a. The diameter of the fiber is
such, for example, 100 .mu.m in the present example, that the fiber
can be disposed at the bottom of the grooves.
Preferably, immediately after the glass fiber is formed, it is
coated with a layer of a synthetic resin composition. In FIG. 1b a
glass fiber 10 is shown whose entire surface is coated with a
coating 11 of a polyamide, for example, Eurelon 2140.RTM., which is
marketed by Schering. In this example, the thickness of the coating
is 10 .mu.m. If desired, the fiber may also be partially coated,
for example on one side, with such a coating. The polyamide is
applied from a solution which contains 25% by weight of polyamide
in a solvent which consists of 65% by weight of n-propanol, 20% by
weight of toluene and 15% by weight of water. The solution is
applied by means of low-pressure extrusion after which the glass
fiber is led through an oven at a temperature of 200.degree. C.
which causes the solvent to evaporate, leaving a polyamide layer on
the glass fiber.
FIG. 2 shows a substrate 21, for example, of
polymethylmethacrylate, provided with ribs 22. The screen shown in
the figure is flat, but the invention may also be applied to a
slightly curved screen. The ribs 22 are provided at the front side
with a lens structure 23. However, dependent upon the desired
optical characteristic of the screen the apexes of the ribs may
have various shapes. Between the ribs 22 there are mainly V-shaped
grooves 24. The ribs and the grooves may be formed on the surface
of the substrate by means of, for example, a replica technique
which is known per se, for example, by means of a synthetic resin
composition which can be cured by UV light. The rear surface of the
substrate (not shown in the Figure) may also be provided with an
optical element, for example, a fresnel structure. In accordance
with this exemplary embodiment, the pitch between the mutually
parallel grooves is 275 .mu.m, i.e. the distance measured between
the deepest points of two successive grooves, the depth of the
grooves is 440 .mu.m.
FIG. 3 shows a sectional view of a glass fiber 10 having a
synthetic resin coating 11, which is located at the bottom of one
of the V-shaped grooves 24. After placing glass fibers in all the
appropriate grooves on the screen, preferably one fiber in each
groove, the synthetic resin coating is heated to a temperature of
180.degree. C., for a short time, for example 1 minute, and
subsequently cooled to room temperature. Heating is done, for
example, by means of radiation at such a wavelength that the
radiation is absorbed by the black glass fibers but not by the
transparent substrate. Thus, the bond between the glass fibers and
the walls of the grooves is formed.
If desired, a reflective layer may be applied to the walls of the
grooves in order to facilitate the internal reflection of the light
in the ribs. In that case, the light-absorbing glass fibers are
bonded to the rear side of such a reflecting layer.
A screen manufactured in accordance with the method described
herein has an attractive appearance and is homogeneously blackened.
The black bands are resistant to wear and to rubbing and cleaning
using cleaning agents. The glass fibers provide a greater rigidity
to the screen which is resistant to the action of moisture, such
that, in particular, the tendency to warp is reduced.
* * * * *